Combination chemotherapy has been used to treat diverse types of cancer (Chabner et al., Nat. Rev. Cancer 5:65-72, 2005). While drug combination is an option for cancer therapy, the reality is that combination chemotherapies have several disadvantages, including (1) distinct pharmacokinetics and tissue distribution of each drug due to differences in each drug's physicochemical properties, and (2) more serious side effects, because each drug may have different toxicity profiles. These disadvantages make dosing and scheduling of each drug a challenging task.